// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#pragma once

#include <cstddef>
#include <cstdint>

#include "crc32c/crc32c.h"

namespace tl {
namespace crc32c {

// Return the crc32c of `concat(A, data[0,n-1])` where `init_crc` is the crc32c
// of some string A. `Extend()` is often used to maintain the crc32c of a stream
// of data.
inline uint32_t Extend(uint32_t init_crc, const uint8_t* data, size_t n) {
  return ::crc32c::Extend(init_crc, data, n);
}

// Return the crc32c of `data[0,n-1]`.
inline uint32_t Value(const uint8_t* data, size_t n) {
  return Extend(0, data, n);
}

inline constexpr uint32_t kMaskDelta = 0xa282ead8ul;

// Return a masked representation of crc.
//
// Motivation: it is problematic to compute the CRC of a string that
// contains embedded CRCs. Therefore we recommend that CRCs stored
// somewhere (e.g., in files) should be masked before being stored.
inline uint32_t Mask(uint32_t crc) {
  // Rotate right by 15 bits and add a constant.
  return ((crc >> 15) | (crc << 17)) + kMaskDelta;
}

// Return the crc whose masked representation is masked_crc.
inline uint32_t Unmask(uint32_t masked_crc) {
  uint32_t rot = masked_crc - kMaskDelta;
  return ((rot >> 17) | (rot << 15));
}

}  // namespace crc32c
}  // namespace tl
